1. Field of the Invention
The present invention relates to an image sensor and, more particularly, to a convex image sensor and a method of forming the sensor.
2. Description of the Related Art
The rigidity of a semiconductor wafer (the resistance of the wafer to deformation) is reduced significantly as the thickness of the wafer is reduced. For example, when the thickness of a semiconductor wafer is approximately one mil, the wafer can be deformed. One application of a very thin wafer is as the photo-sensing element of an optical image sensor.
FIG. 1 shows a cross-sectional diagram that illustrates a prior art optical image sensor 100. As shown in FIG. 1, optical image sensor 100 includes a very thin wafer 110, and an array of photodiodes and associated photo-sensing circuitry 112 that are formed on wafer 110. Imager 100 also includes a base structure 114 that has a concave surface 116 that supports wafer 110.
In addition, image sensor 100 also includes a single low-cost lens 120 that focuses incoming light 122 on a curved focal plane 124. Curved focal plane 124, in turn, has a convex outer shape that approximately matches the shape of concave surface 116. As a result, the non-rigid structure of a very thin wafer allows the array of photodiodes to be placed on the curved focal plane 124 of low-cost lens 120, thereby forming a low-cost imager with a substantially improved optical quality.